Biphenotypic Acute Leukemia versus Myeloid Antigen-Positive ALL: Clinical Relevance of WHO Criteria for Mixed Phenotype Acute Leukemia

Figure 1

Histology and immunohistochemistry (IHC) studies on bone marrow biopsies. Flow cytometry analysis and FISH studies on peripheral blood specimens from (a) diagnosis and (b) relapse at 24 weeks. (a) This series shows the phenotype of B-cell ALL, staining positive for CD79a and TdT but negative for MPO. Flow cytometry shows a blast population that is strongly CD19 positive and weakly CD10 positive. The FISH study shows two blast populations: a heterozygous deletion in 42.5% of nuclei [9p-(CDKN2Ax1,D9Z1x2)] and a homozygous deletion in 36% of nuclei [9p-x2(CDKN2Ax0,D9Z1x2)]. (b) This series demonstrates a myeloid leukemia phenotype with strong MPO staining and lack of CD19 and CD10 expression by flow. The FISH shows persistence of a heterozygous CDKN2A gene deletion [9p-(CDKN2Ax1,D9Z1x2)] present in 75.5% of nuclei tested. ALL, acute lymphoblastic leukemia; CDKN2A, cyclin-dependent kinase inhibitor 2A; FISH, fluorescence in situ hybridization; TdT, terminal deoxynucleotidyl transferase; MPO, myeloperoxidase.

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